The present invention relates to an apparatus and method for orthodontic treatment. The embodiment of the orthodontic bracket designed consists of two tie wings or projections which form a rectangular slot or groove. The slot is designed to hold the wire which connects all of the teeth in a dental arch. The tie wings typically hold the archwire by means of a wire or elastic ligature. The twin bracket has proven to be an excellent way to move teeth in three planes of space. The specific movements are rotation, vertical change, and torque. The two tie wings help facilitate the rotation of the tooth. The slot in each of the tie wings allows for movement of teeth vertically and also allows for tipping of the root or crown. The slot is rectangular so as to be able to accommodate a rectangular wire which allows an individual tooth to be moved in a third dimension that torques or tips the root of the tooth.
The orthodontic bracket appliance that is in common use today began with gold brackets soldered to gold bands that were cemented around each tooth. The dimension of the slot was 0.022 inch (height) by 0.028 inch (depth). Gold wires and bands were abandoned in the 1950s and were replaced with stainless steel. Because gold is a softer metal than stainless steel, manufacturers developed bracket slots of 0.018 inch by 0.028 inches to accommodate the stiffer stainless steel wires. This change in wire size was required to duplicate the forces produced by the softer gold wires.
Orthodontists were reluctant to abandon the 0.022 slot out of tradition. As a result, orthodontic brackets are still manufactured in two slot sizes. Most manufacturers offer both 0.022 slot and 0.018 slot orthodontic brackets. The common method of manufacturing the two sizes of slots is to cast a bracket that can be cut to both bracket sizes. When metal injection molding is used, it only produces one bracket size.
When using the 0.022 slot twin brackets, orthodontists begin treatment with small round archwires ranging in size from 0.014 inch to 0.020 inch. Treatment is initiated with small archwires which are flexible and facilitate the easy rotation and vertical movement of teeth. The round archwires are followed by rectangular archwires. The rectangular archwires are used in finishing treatment and provide for proper torque and angulation. These finishing archwires are usually of the rectangular dimension, 0.022 inch by 0.025 inches. The final archwires are placed with several bends, specifically made to move each tooth to its ideal position. In the 1970's inta “straight-wire” bracket was introduced. It was fashioned to eliminate the need for the many bends in the finishing wires. The bracket slots had different rotations, tips, and torque for each tooth, essentially a prescription for each tooth.
The larger slot size works more efficiently in the early stages of treatment because it minimizes friction and binding forces when used with round archwires. The smaller slot size works best with the finishing wires because a finishing wire of 0.018 inch by 0.022 inches is not as stiff as a finishing wire of 0.022 inch by 0.025 inches. The larger archwire is so inflexible it is almost impossible to place in the mouth. Most orthodontists use a finishing archwire of 0.018 inch by 0.022 inches. If the finishing wire does not fill the slot, then the wire does not produce the precise movement required. Orthodontic brackets have been unable to take full advantage of the significant changes in dental materials such as nickel-titanium and titanium-molybdenum archwires developed in the 1990's. Manufacturers have focused on adding features to existing bracket slot designs such as selfligating doors to reduce some of the friction. The nickel-titanium archwires are flexible and more resilient and can consequently aid in reducing binding forces. The accuracy of metal injection molding and the advances in archwire technology drive the innovative changes that have been incorporated in the present invention.